1. Field of the Invention
This invention relates in general to a riser system that extends between a floating drilling or production platform and a subsea well, and in particular to a union connection at the top of the riser string.
2. Description of the Prior Art
In U.S. Pat. No. 4,403,658, issued Sept. 13, 1983, Bruce J. Watkins, a single stab union is shown for an offshore drilling or production platform. In the patent, at the top of the riser run or string, a termination head is adapted to be received within a female termination housing. The termination housing has a number of radial ports that register with passages located in the termination head. These ports contain high pressure fluid for transmission between the vessel and the subsea well. If it is necessary to disconnect the lower end of the riser from the subsea well temporarily, the termination head can be pulled upward from the termination housing. The lines or hoses connected to the termination housing can remain in place, connected to the housing.
In the Watkins patent, the housing has a longitudinal bore with a conical taper. The termination head has a mating conical exterior that seats within the bore of the termination housing. While connecting the lower end of the riser string to the subsea well and after connection, the termination housing is suspended on cables lowered from winches mounted on the vessel. The housing is thus under large tension forces which might cause it to ride up on the termination head. The conical seat may jam, making it very difficult to pull the termination head from the termination housing.